1. Field of the Invention
The present invention relates to a production method for a water-absorbing resin composition. In more detail, the present invention relates to a production method for a water-absorbing resin composition, having a mixing step for mixing water-absorbing resin particles and additive particles.
2. Description of the Related Art
A water-absorbing resin, both a natural product and a synthesis product, generally has hydroscopicity, and as a natural product, starch and agar, or the like is known; and as a synthetic product, polyvinyl alcohol, polyacrylic acid (salt), polyacrylamide, polyethyleneimine, or the like is known.
A water-absorbing resin is widely used recently, aiming at absorbing body fluid, in the fields of hygienic goods such as a paper diaper or a sanitary napkin, so-called an in continence pad and the like. As such a water-absorbing resin, for example, partially neutralized cross-linked polyacrylic acid, a hydrolyzed starch-acrylonitrile graft polymer, a neutralized starch-acrylic acid graft polymer, a saponified vinyl acetate-acrylic acid ester copolymer, a hydrolyzed acrylonitrile copolymer or an acrylamide copolymer, or cross-linked body thereof, a cross-linked polymer of a cationic monomer or the like is known.
Characteristics which a water-absorbing resin should have includes water absorption characteristics such as excellent absorbency or absorption rate, and fluid permeability in contacting with aqueous fluid such as body fluid or the like, or handling property such as excellent fluidity so as not to adhere to apparatus or the like, even by moisture absorption, in preparation of an absorbing body by fabrication with a water-absorbing resin and a fiber substrate or the like, or in production or conveyance of a water-absorbing resin. Furthermore, with demand increase in an adult diaper accompanying the aging, characteristics for furnishing additional functions such as antibacterial or deodorant property to a water-absorbing resin has also been required.
To obtain various characteristics as described above, technology for the addition of additive particles aiming at furnishing various functions to water-absorbing resin particles has been proposed. For example, EP No. 629411, JP-A-2003-176421, and JP-A-11-286611 disclose technology to improve anti-gel-blocking property or fluid permeability of a diaper in absorbing urine; JP-A-2000-93792, U.S. Pat. No. 6,124,391, U.S. Pat. No. 5,985,944, JP-A-9-241322, JP-A-64-4653, and US-A-2005/113252 disclose technology to improve anti-caking characteristics; and WO-A-2005/10102, JP-A-9-248454, EP No. 1257596, and JP-A-10-120921 disclose technology for furnishing antibiotic property or deodorant property. In addition, because water-soluble resin particles similarly generate caking, similar solving methods by cohesive fine particles have been proposed. In addition, there are many proposals on methods for improving property by the addition of additive particles other than cohesive fine particles, to water-absorbing resin particles, for example, technology for the addition of powder of water-soluble metallic soap (US-A-2005/118423), or technology for the addition of powder of a polyvalent metal salt (US-A-2006/73969, U.S. Pat. No. 6,300,275), has been proposed.
And, as a mixing method for these additive particles and a water-absorbing resin, dryblend (mixing of power itself) is generally carried out, and many continuous type or batch type powder mixers have conventionally been proposed. As such powder mixers, for example, a paddle blender, a ribbon blender, a rotary blender, a jar-tumbler, a plunger mixer, a cylinder-type mixer, a V-shaped mixer, a ribbon-type mixer, a screw-type mixer, a double arm-type mixer, a crushing-type mixer, a channel-type mixer, a harrow-type mixer, an airflow type mixer and the like are known. In addition, in such mixing, a method for simultaneous granulating and mixing of a water-absorbing resin has been proposed (US-A-2006/73969)